Top Photo: The Presidential Pallace in New Delhi, enveloped in smog | Altaf Qadri/Associated Press

According to a study published by India's Center for Science and Environment, the city with the poorest air quality is actually Delhi, where air pollution this winter was as much 60-times higher than the level considered safe.

The most harmful airborne pollutants, categorized innocuously enough as PM2.5, averaged 575 micrograms per cubic meter in the Indian capital from November to January.

That compared with a — still dangerous — concentration of 400 micrograms at peak levels in Beijing over the same period.

PM2.5 refers to the diameter in microns of nasties such as ammonia, carbon, nitrates and sulfate — particulates small enough to pass into the bloodstream and cause diseases such as emphysema and cancer.

A city such as London has an average PM2.5 level of 20 micrograms, which is considered safe.

The CSE report goes on to say that Beijing stands a chance to permanently relieve itself of the title of world's smoggiest city, if it continues to make "consistent and aggressive efforts" to improve its air quality. The report says Beijing's measures stand in stark contrast to Delhi's weak stringency and enforcement of pollution controls.